Method for producing electrode material for lithium ion batteries

Abstract

A method for producing a graphite material for lithium ion batteries, including a step for exothermically graphitizing a carbon material by directly applying an electric current therethrough. The carbon material is obtained by heating at a temperature in the range of 800° C.-1500° C. inclusive and subsequently pulverizing an organic carbon starting material, has a compact powder resistivity of 0.3 Ω cm or less when compressed to a density of 1.4 g / cm3, has an angle of repose in the range of 20° to 50° inclusive, and has a particle size (D90) in the volume-based particle size distribution measured using laser diffraction of 120 μm or less. The average surface interval (d002) of a surface (002) of the carbon material after graphitization, measured using x-ray diffraction, is in the range of 0.3354 nm-0.3450 nm inclusive.

Description

CROSS REFERENCE TO RELATED APPLICATIONS[0001]This application is a National Stage of International Application No. PCT / JP2012 / 077038, filed Oct. 19, 2012, claiming priority from Japanese Patent Application No. 2011-232291, filed Oct. 21, 2011, the contents of all of which are incorporated herein by reference in their entirety.TECHNICAL FIELD[0002]The present invention relates to a graphite material.BACKGROUND ART[0003]As a power source of a mobile device, a lithium ion secondary battery is mainly used for the reason of its high-energy density and long cycle life. The function of the mobile device or the like is diversified, resulting in increasing in power consumption thereof. Therefore, a lithium ion secondary battery is required to have an increased energy capacity and, simultaneously, to have an enhanced charge / discharge cycle characteristic. Further, there is an increasing demand recently for a secondary battery with a high output and a large capacity for electric tools such as ...

AI Technical Summary

Benefits of technology

The present invention provides a method for producing a high-quality graphite material that is stable, has low impurities, and is cost-effective. This material is useful as an electrode material for lithium ion batteries. When used as a negative electrode, the material allows for smoother insertion and release of lithium ions, resulting in superior battery performance in terms of input-output characteristics and cycle lifetime.

Problems solved by technology

The function of the mobile device or the like is diversified, resulting in increasing in power consumption thereof.

In particular, in applications for automobiles, such as battery electric vehicles (BEV) and hybrid electric vehicles (HEV), a long-term cycle characteristic over 10 years and a large current load characteristic for driving a high-power motor are mainly required, and a high volume energy density is also required for extending a driving distance, which are severe as compared to mobile applications.

When an electrode made of such a material is charged, the electrode expands only in one direction, which degrades the performance of the electrode such as current characteristics and cycle life.

Further, as a demerit of high crystallinity, the surface of the natural graphite is active, and hence a large amount of gas is generated during initial charging, which decreases an initial efficiency and further degrades a cycle life.

However, it is very difficult for the material to satisfy the requests such as a large current and an ultralong-term cycle characteristic of a large battery as described above.

In addition, natural graphite has a problem relating to quality stability because it contains a large amount of metallic impurities such as iron.

However, it is difficult to achieve the cycle characteristics for a long period of time which are required for a large battery due to problems such that the conductive contact of the electrode powder with each other tends to degrade.

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